These two terms differ in a number of ways, but on a basic level they can be said to differ in terms of scope and specificity. Text is a highly specific term and refers to the written word as such. Context, as a term, can be employed on various levels within a work of literature and outside a work of literature.
In literary studies, the term, "text," refers solely to the written word on the page. When discussing text, we are discussing that actual and literal words used by a writer. Thus, when we use the term we are not discussing what is implied (which would be subtext). We are instead only referring to what is explicitly and physically on the page.
While text can imply and text can express, our reference to text nonetheless is always to the actual words that are being interpreted to imply and express. An analogy for this situation might be to compare text to a painting. The painting is a physical object capable of communicating ideas and emotions to an audience, but when we talk about the painting we are always referring to its physical being, its surface and actual existence. We interpret that physical object and thereby discern its meaning.
Text can also be used in generalization to describe a book (as in, "let us turn to the text itself for an answer").
Context refers to a situation (or surroundings). This term can describe the situation created within a narrative (or within a text). If a character is stranded on a desert island after a boat has sunk, we would describe this state of affairs as the context.
Also, context can describe the situation within which a book has been written. A novel written after WWII concerning relations between the U.S. and Russia has a specific cultural and political context that provides a framework wherein we can discern some particular meaning(s) in the text.
"Understanding the context in which a work of literature was produced often leads to a deeper understanding of the work itself; for instance, understanding the social and economic position of women in the early Nineteenth Century can provide a greater insight into the characterizations of women in Jane Austen’s novels" (eNotes).